Bumping React to 15.6.2 (MIT license) (apache#3569)

I think that leaves only immutable.js with the ASF-incompatible PATENTS clause

I asked for a 3.8.x MIT release of the immutable lib here:
immutable-js/immutable-js#1309

superset/assets/package.json

@@ -62,16 +62,16 @@
     "moment": "^2.14.1",
     "mustache": "^2.2.1",
     "nvd3": "1.8.6",
-    "prop-types": "^15.5.8",
-    "react": "^15.5.1",
+    "prop-types": "^15.6.0",
+    "react": "^15.6.2",
     "react-ace": "^5.0.1",
     "react-addons-css-transition-group": "^15.6.0",
     "react-addons-shallow-compare": "^15.4.2",
     "react-alert": "^1.0.14",
     "react-bootstrap": "^0.31.2",
     "react-bootstrap-table": "^4.0.2",
     "react-datetime": "^2.9.0",
-    "react-dom": "^15.5.1",
+    "react-dom": "^15.6.2",
     "react-gravatar": "^2.6.1",
     "react-grid-layout": "^0.14.4",
     "react-map-gl": "^3.0.4",
@@ -125,8 +125,8 @@
     "less": "^2.6.1",
     "less-loader": "^4.0.3",
     "mocha": "^3.2.0",
-    "react-addons-test-utils": "^15.5.1",
-    "react-test-renderer": "^15.5.1",
+    "react-addons-test-utils": "^15.6.2",
+    "react-test-renderer": "^15.6.2",
     "redux-mock-store": "^1.2.3",
     "sinon": "^4.0.0",
     "style-loader": "^0.18.2",